The present invention relates to dampers. More particularly, our invention relates to self-centering, bi-directional dampers that may be used, for example, in connection with controlling the operation of hydrostatic transmissions, such as those employed in commercial lawn mowers.
Dampers have long been known. Generally speaking, traditional damper designs employ a tubular body that defines an elongated, closed chamber filled with an incompressible fluid or liquid. A piston and shaft assembly are disposed within the damper body chamber so that one end of the shaft extends out of the chamber. The dampening rate of the damper is determined by the rate of fluid flow across the piston assembly as the piston assembly is moved relatively with respect to the damper body. Valves or other means are carried by the piston assembly and serve to control the fluid flow across the piston assembly.
So-called, non-cavitating dampers are also known. They provide an important advantage, vis-avis, traditional damper designs, in that they eliminate the problems of "cavitation" or "free fall" inherent in the traditional damper designs. Non-cavitating dampers are orientation insensitive in use and may thus be utilized in many more and different applications than traditional dampers.
The long recognized primary function of dampers has been to dampen the movements of relatively fixed and relatively movable members. Nevertheless, however, dampers have not been cast competitive for use before with the hand operated levers that are often employed to control the operation of hydrostatic transmissions such as those used to power commercial lawn mowers. These operating levers are usually pivotally mounted on the mower, at their lower ends, and when the transmissions are in neutral, that is, are not powering the lawn mower, the levers are usually disposed vertically in an upright, centered position. The operator moves the operating lever from its centered or "neutral" position, either forward or rearward, to control the direction of movement--in the forward or rearward direction--and the speed of movement of the mower.
In the past, a variety of spring arrangements have been used to assure that the operating lever is returned to its neutral or centered position after the operator has moved the lever and then let it go. While the prior spring arrangements generally worked as they were intended, they did and do have serious disadvantages. The springs could and did cause the operating lever to return too quickly from a "fast" forward or "fast" rearward operating position to its neutral or centered position after the operator releases the lever. This can cause the mower to dip abruptly and/or to stop too suddenly. Such dipping and/or abrupt stoppages pose serious safety hazards for the operator. Also, the mower transmission may suffer serious "shock" damage due to the spring arrangement causing the operating lever to return through and pass its neutral position. Current spring arrangements also tend to be relatively expensive because of the number of parts and the time and labor costs involved in manufacturing and installing.
Using traditional dampers, in place of spring arrangements, would not appear to provide a practical solution to the problems arising from employing current spring arrangements to re-position the operating level back to its neutral position. To be effectively used with most operating levers, the damper would have to be oriented horizontally or nearly horizontally. Such an orientation would result in serious potential cavitation problems. Non-cavitating dampers appear to perhaps be a possible, partial solution, but they still have the potential of permitting the operating lever to return through and past its neutral position.